Shock absorber provided with a stress limiting device



Patented Apr. 25, 1939 PATENT OFFICE SHOCK ABSORBER PROVIDED WITH ASTRESS LIMITING DEVICE Rene Lucien Levy, Montrouge, France, asslgnor toSocit d'lnventlons Aeronautlques ct M- caniques S. I. A. M., Frlbourg,Switlerland Application January 30. 1937, Serial No. 123,264 In FranceFebruary 24, 1938 3Claims.

The present invention relates to shock absorbers and more particularlypertains to hydraulic shock cushioning devices for use in connectionwith airplanes.

5 Numerous known shock absorbers are based on a principle 01' operationwhich consists in varying, during the stroke of a piston, the sectlon ofthe passageway tor a fluid, either by means 01' a rod of variable crosssection, passing through an opening or constant diameter in a diaphragmor by grooves provided in a piston rod, or by any other suitable means.

Shock absorbers of this type, judiciously devised provide for theabsorption 01 energy.

It is however to be noted that the result obtalned from such devicesdepends on the relative speed imparted, at the time of operation, to themovable element of the shock absorber relatively to the fixed element.In case the shock absorber is fitted on an aircraft, for instance on thelanding chassis of an airplane. the results obtained essentially dependon the vertical speed or fall upon landing. For instance, with a givenshock absorber, constructed and adjusted to be responsive to a speed offall of about 3 meters per second, one result would be obtained,whereas, for the same adjustment, 9. speed of fall in the order of 3meters 50 per second would provide a dinerent result.

In the past, the shock absorbing devices in use in aviation did not havethese inconveniences, as airplanes landed substantially at the maximumvertical speed possible and the shock absorbers were devised andadjusted for this speed.

Now the landing speeds of airplanes vary.

Consequently, by adiusting the shock absorber in the usual manner, thereis a risk of the plane being insufiiciently cushioned when rolling onthe ground or flying oil.

The present invention is adaptable to any type of oleo-pneumatic shockabsorber and includes, a stress limiting device which prevents theabsorption of energy from rising above a value determined by themanufacturer.

The single figure oi the drawing diagrammatically illustrates theapplication or the invention to a shock absorber of a type similar tothat forming the subject-matter of the French Patent No. 31, of December1934.

Referring to this figure, it will be seen that,

when the piston l0 moves in a cylinder II, in the direction of the arrowI, the shock absorbing efiect occurs when the liquid passes through thenarrow orifice l2, the valve it being closed. The liquid deliveredpasses in a conduit l4, into a compartment ll, through valves I, whichare open. .According to the invention, a valve I! loaded with a springI8, is fitted in the piston ll about the tube ll.

If the pressure in the compartment ll exceeds 5 a definite value thevalve i1 is pushed back, and moves away irom its seat Ill and oflers tothe liquid. through the piston, an additional passageway. Upon returnmovement of the piston ll, the liquid in compartment l5 passes into com-10 partment I! through a groove 2| formed in the periphery of the tubell.

The above described embodiment is given by way of example only, as itwill be understood that the invention can be carried out in various man-15 ners according to the type 01' shock absorber to which it will beapplied.

. What I claim as my invention and desire to secure by Letters Patentis: 1. In a shock absorber for the landing chassis go of airplanes, acylinder, a piston movably mounted in said cylinder in response to theforce to be cushioned and providing a compartment on each side of thepiston, said piston having a central opening, liquid in saidcompartments, a con- 25 duit fixed to the base of said cylinder andextending through said piston, said conduit having a passage so as toprovide an opening communicating from the first compartment into theinterior of said conduit so that relative move- 30 ment of said pistontowards the base of said cylinder will be cushioned by the liquidpassing from the first compartment through said passage, a valvearranged in the opening oi said piston embracing said conduit, yieldablemeans urging said 35 valve to a position to normally close the openingin said piston, the force of said yieldable means being such that thevalve is opened to provide an additional passage for the liquid fromthefirst compartment only when the pressure therein 40 reaches apredetermined value, and said conduit having a longitudinally extendinggroove of smaller area than either of said passages to permit return oithe liquid to the first compartment on the re-bound movement of thepiston. I 45 2. In a shock absorber tor the landing chassis ofairplanes, a cylinder, a piston movably mounted in said cylinder inresponse to the force to be cushioned and providing a compartment oneach side of the piston, liquid in said compart- 50 ments, means havinga first system ororifices to permit liquid to be delivered from thefirst compartment during relative movement of the piston to provide acompression stroke in the first compartment, means providing a secondsystem 55 oi orifices for permitting the liquid to he delivered from thesecond compartment during opposite movement of the piston, said secondsystem otorifices havinzaunitareaoipassage smaller thanthatoithefirstsystemotorifices,avalve adapted to be opened only durin:the first mentioned movement oi the piston so that an additlonaljopeningis provided to permit liquid from the first compartment to passtherefrom and yieldahle means for normally closing said valve during thefirst movement of the piston but permittin: the valve to open when thepressure in the first compartment exceeds a predetermined value.

3. In a shock absorber for the landing chassis oi airplanes, a cylinder,a piston movahly mounted in said cylinder in response to the force to hecushioned and providing a compartment on each side of the piston, liquidin said compartments, means having a first system oi. orifices to permitliquid to be delivered from the first compartment during relativemovement of the piston to provide a compression stroke in the firstcompartment, means providing a second system of orifices for permittingthe liquid to be delivered from the second compartment during oppositemovement of the piston, said second system of orifices having a unitarea of passage smaller man that of the first system of orifices, avalve adapted to be opened only during the first mentioned movement ofthe piston so that an additional opening is provided to permit liquidfrom the first compartment to pass therefrom, a spring for normallyurging said valve to a closed position during the compression of theliquid in the first compartment, and the force of said spring being suchthat it permits the valve to open when the pressure in the firstcompartment exceeds a predetermined value.

RENE Lucian LE Y. 2o

